Warmup Problem

Algebra Level 2

What is 9 9 2 9 8 2 ? 99^2 - 98^2 \, ?

Note: Try it without using a calculator.

198 199 197 187

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73 solutions

Ritu Roy
Nov 12, 2014

{ a }^{ 2 }-{ b }^{ 2 }=(a+b)(a-b)\\ { 99 }^{ 2 }-{ 98 }^{ 2 }=(99+98)(99-98)\\ \quad \quad \quad \quad =(197)(1)\\ \quad \quad \quad \quad =\boxed { 197 }

Best answer.

Christopher Patridge - 6 years, 6 months ago

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You mean it's the best solution. All correct answers are the best.

William Park - 6 years, 5 months ago

difference of two squares. i really forgot it. i just guess for my answer and it is correct!

Stephen Gamuzaran - 6 years, 6 months ago

4th standard algebra fomula a^2 - b^2 =(a-b) (a+b)

Everly Marweiñ - 6 years, 4 months ago

very accurate answer

Siva Balan - 6 years, 6 months ago

i really forgot the method to solve it nw i got it

Aathira Menon - 6 years, 6 months ago

good answer

Afaq Rind - 6 years, 6 months ago

I,ve got it

Tonny Rahu - 6 years, 5 months ago

nice solution,but i prefer use (100-1)^2-(100-2)^2 to solve it cause to me ,it is much easier to do this by mental calculation

Loki Come - 6 years, 6 months ago

99^1-98^1 woulkd give us 1 so y cant the same logic be apllied here i mean both have increased by same proprtion so the difference should remain same

Fida Gul - 6 years, 6 months ago

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because that only works with addition and subtraction, but this involves multiplication.

Randy Dela Cruz - 6 years, 6 months ago
Simon Fermor
Nov 16, 2014

9 9 2 9 8 2 = ( 98 + 1 ) ( 98 + 1 ) 9 8 2 99^2 -98^2= (98+1)(98+1)-98^2 = 9 8 2 + 98 + 98 + 1 9 8 2 = 2 98 + 1 = 197 =98^2+98+98+1-98^2=2*98+1=197

This is needlessly complicated. Just use the standard factorization of the difference of two squares.

Michael Hardy - 6 years, 5 months ago

The Same with Me! Greets bro! :)

İsmail Açıkel - 5 years, 5 months ago

i like your solution

Karel Bachri - 6 years, 6 months ago
Arjuna Sarathy
Nov 17, 2014

n^2 - (n-1)^2 = 2n-1

Minh Nguyen
Nov 26, 2014

Imagine a 98x98 square fitting inside of a 99x99 square. The remaining open space is the difference, which yields a row of 99, a column of 99, and an overlap. Thus 99+99-1=197

Thank you for this visual solution!

Susan Kervin - 6 years, 3 months ago

It's been a while since college algebra, so: mentally, 100^2=10,000. 99^2 is one 100 and one 99 less than that: 9,801. 98^2 is two 100's and two 98's less than 10,000: 9,604. The difference would be 200 if it weren't for the fact that 4 is 3 more than 1; therefore, the difference is 3 less than 200.

Hitoshi Yamamoto
Nov 16, 2014

99^2 - 98^2 = (98+1)^2 - 98^2 = (a+1)^2 - a^2 = a^2 - a^2 + 2a + 1= 2*98 + 1 = 196 +1 = 197

a^2 - (a-1)^2 = (a + (a-1))(a - (a-1)) = (2a -1)(1) = 2a -1 here: a = 99; So: 2(99) - 1 = 197

Talha E. Siddiqi - 6 years, 6 months ago

9 9 2 9 8 2 = ( 99 + 98 ) ( 99 98 ) = ( 197 ) ( 1 ) = 197 99^2-98^2=(99+98)(99-98)=(197)(1)=\boxed{197}

Hence: a^2 - (a-1)^2 = a + a -1

Talha E. Siddiqi - 6 years, 6 months ago
Jacob Heyn
Nov 12, 2014

A pattern of squares is that

a^2=b^2+(a+b)

Where a is the next number and b is the previous

Samir Martins
Dec 2, 2014

99²-98²=

(98+1)(98+1)-98²=

98²+2(98)+1²-98²=

2(98)+1= 197

Dileep Kumar
Nov 16, 2014

Difference of two squares formula: 99^2 - 98^2= (99 + 98)(99 - 98)= (197)(1)= 197

Daniel Power
Mar 5, 2015

I did it by noticing the pattern of the difference in powers. I noticed that if I did

3 2 2 2 = 5 3^{2} - 2^{2} = 5

4 2 3 2 = 7 4^{2} - 3^{2} = 7

5 2 4 2 = 9 5^{2} - 4^{2} = 9

And so on. So I realized that the given the format a 2 b 2 a^{2} - b^{2} the answer was always ( b × 2 ) + 1 (b \times 2) + 1

From there it was as easy as ( 98 × 2 ) + 1 = 197 (98 \times 2) + 1 = 197

Kanchan Dey
Dec 6, 2014

99~2-98~2 =(99+98) (99-98)=197X1= 197Write a solution.

Chew-Seong Cheong
Nov 17, 2014

9 9 2 9 8 2 = ( 98 + 1 ) 2 9 8 2 99^2-98^2 = (98+1)^2 - 98^2

= 9 8 2 + 2 × 98 + 1 2 9 8 2 \quad \quad \quad \quad = 98^2 + 2\times 98 + 1^2 - 98^2

= 196 + 1 = 197 \quad \quad \quad \quad = 196 + 1 = \boxed {197}

Gaige Frederick
Nov 15, 2014

99^2-98^2=9801-9604=197

99^2 - 98^2=(99+98) (99-98) = 197 (1) = 197

N T
Dec 19, 2015

I forgot about difference of two squares, so I did this:

99^2 = (98+1)(98+1) = 98^2 + 98 + 98 + 1

so

99^2 - 98^2 = 98^2 + 98 + 98 + 1 - 98^2 = 98 + 98 + 1 = 197

Garrison Wynn
Dec 19, 2015

Best way to work this out is visually, Imagine a 99 X 99 pixel grid then a 98 X 98 pixel grid on top of it, there will two 1-pixel lines forming an L-shape which give the answer, The lines are each 99*1 but with one common pixel. ie. ((99 X 1) X 2)-1

William Sydnor
Mar 6, 2015

As a matter of pattern, if (2^2)-(1^2) = 3 and 1+2=the same, and (5^2)-(4^2)= 9and 5+4 =the same, and (7^2)-(6^2)=49-36=13=7+6, and so one, a pattern can be seen that a number squared minus one less than itself squared is equivalent to both numbers added, therefore, simply though pattern recognition, without actually having to actually "do" the equation itself, we can recognize that (99^2)-(98^2) is equivalent to 99+98, in other words 197. So yes, a calculator would have taken the fun out of that.

Shibi Chakku
Feb 18, 2015

Difference between the squares of two consecutive numbers will be the sum of the two numbers always.

(a+1)^2 -a^2 = 2a+1

Kevin Gunawan
Feb 1, 2015

99^2 - [(99-1)^2]

Omar Mansour
Jan 23, 2015

99^2 - 98^2 =99 99 -98^2 =(98+1)(98+1) -98^2 =98^2+2 98 +1 -98^2 =2*98 +1 =197

Amr Ahmed
Jan 21, 2015

99^2 = (99 * 99)-(98^2) 99 * 99 = (98 + 1) (98 +1) - 98 98 = [(98 * 98) + (98 * 1) + (98 * 1) + (1 * 1)] - (98 98) =98+98+1 =197

Yanto Sama
Jan 19, 2015

(a+b)^2 = (a+b)(a-b), so it becomes 98+ 99 = 197

Pola Botros
Jan 12, 2015

X^2-(X-1)^2 = X+(X-1) 99^2-98^2 =99+98=197

Qonitah Jannah
Jan 11, 2015

We use concept: a^2-b^2 = (a+b) (a-b) So, Obviously that 99^2 - 98^2 = (99+98)(99-98) = 197.

Danny Pearson
Jan 9, 2015

I just did 99 + 98

Lar Seward
Jan 7, 2015

Difference of two squares results in 197.

Ki Chan
Jan 7, 2015

(Sequential exponential pattern)

n=1 n^2=1 (n+1)^2 = n^1 +n x 2 +1 4 = 1 + 2 + 1 4=4

sub in 98 n^2-n^2+ n x 2 + 1 = the difference of the two squares which is 197

Garvin Goei
Jan 5, 2015

First, you should know the pattern of difference of two square numbers:

a^2 - b^2 = (a+b) (a-b)

Just follow the pattern/formula and you will get the answer.

Praveen Velamala
Dec 31, 2014

x^2-y^2= x+y iff x=y+1

Mahmoud Ibrahim
Dec 25, 2014

99^2-98^2=(98+1)(98+1)^2-98^2 =98^2+98+98+1-98^2=98+98+1=196+1=197

Dhani Larasati
Dec 24, 2014

Why dont we just use easiest solution? 99^2 - 98^2 = 99 + 98 = 197

square of a number s d sum of preceding square nd its double +1 ....... i.e.......2^2 = 4 .......3^2= 4+(2 2)+1..... (3^2)-(2^2) = (2 2)+1... ......in d same way ....(99^2) - (98^2) = (98*2)+1...

Akanksha Sangode
Dec 15, 2014

If n^2 is known, (n+1)^2 = n^2 + 2n + 1

Sajid Mamun
Dec 14, 2014

The nth term for the differences between squares is 2n+1 . The question asks for the difference between the 98th and 99th squares, so we substitute 98 as n to find the 98th difference.

(2)98+1 = 197

Let a=98. Then 99^2 - 98^2 = (a+1)^2 - a^2 = a^2 + 2a + 1 - a^2 = 2a + 1 = 2a+1 = 2(98) + 1 = 197

A Solution for the absolute diferance of any 2 consecutive squares

(99+98)(99-98)=197

(100-1)^2-(100-2)2= 100^2+1-200-100^2-4+400
=197

let x = 99, then x^2 - (x-1)^2 = x^2 - (x^2-2x+1)=2x-1=2*99 - 1 = 197 =D

Muhilan Sathya
Dec 7, 2014

(a^2)-(b^2)=(a+b)(a-b) =(99^2)-(98^2)=(99+98)(99-98)=197

Kevin Boban
Dec 7, 2014

Write a solution.

Sam Friedman
Dec 6, 2014

a^2 - b^2 = a + b

sorry this is wrong 5^2-3^2 not equal 2 but 16

Pola Botros - 6 years, 5 months ago
Jerome Yuen
Dec 5, 2014

I just added 99 and 98 together. Is it logical to u guys?

Rico Carreon
Dec 3, 2014

99^2 = 99 * 99 = 9801 ;98^2 = 98 * 98 = 9604 ;9801-9604 = 197

محمد رضا
Nov 28, 2014

99^2 - 98^2 = (98+1)^2-98^2 = (98^2 + 2*98 +1) - 98^2 = 197

Sabyasachi Sarkar
Nov 27, 2014

(100-1)^2-(100-2)^2=(100^2-200+1-100^2+400-4)=197

Naveen Pentapelli
Nov 27, 2014

99^2 - 98^2

= (100-1)^2 - (100-2)^2 - Step 1

Using the formula (a-b)^2 = a^2-2ab+b^2, we can compute step 2 to be

9801 - 9604 = 197

Osama Elabady
Nov 27, 2014

(98+1)^2-(98^2)= (98^2)+98+98+1-(98^2)

Daddhie Mhelpotss
Nov 24, 2014

99²-98²=197 (99x99)-(98x98) =197 9801-9604 = 197

SIMPLE SOLUTION ^^

Manuj Dagar
Nov 23, 2014

Simple if it is square of both then the difference is the sum of them.Like 99²-98²=99+98 =197

Aditya Gupta
Nov 22, 2014

99^2-98^2 =(98+1)^2-98^2 =98^2+1^2+2 98 1-98^2 =1+196 =197

Bareera Samad
Nov 21, 2014

99^2=98^2+98+99 so 99^2-98^2=98+99=197

Hanta Julian
Nov 20, 2014

If a=2 and b=1, then

x = a 2 a^2 - b 2 b^2
x = 2 2 2^2 - 1 2 1^2
x = 4 - 1
x = 3
y = a + b
y = 2 + 1
y = 3

Then

x = y
a 2 a^2 - b 2 b^2 = a + b
X = 9 9 2 99^2 - 9 8 2 98^2
Y = 99 + 98
X = Y
9 9 2 99^2 - 9 8 2 98^2 = 99 + 98

So

X = 99 + 98
X = 197
Will Lopez
Nov 20, 2014

Ritu Roy knows whatsup

Sahad Parammal
Nov 19, 2014

The difference between squares of two positive consecutive numbers will always be the sum of those two numbers. So 99^2-98^2=99+98=197

Kiều Linh
Nov 18, 2014

99^{2} - 98^{2} = (98 + 1)^{2} - 98^{2} = (98^{2} +2 98+1) - 98^{2} = 2 98 + 1 = 197

Sanjay Singh
Nov 17, 2014

in this way too, we can solve it (100-1)^2 - (100-2)^2 by using (a-b)^2 formula we can solve

Stevenson Pascua
Nov 17, 2014

a^2-b^2 = (a+b)(a-b) 99^2 - 98^2 = (99+98)(99-98) =197(1) = 197

MD Ashik Ullah
Nov 17, 2014

a^2-b^2=(a+b)(a-b) 99^2-98^2=(99+98)(99-98) =197*1 =197

Logic/geometric solution : Draw a square with a 98 side into a 99 side one : result of exclusion is a horizontal stripe 99×1 and a vertical stripe 98×1. So answer is 98+99=197

Amir Asaad
Nov 17, 2014

99^2 - 98^2 = 99^2 - (99 - 1)^2 = 99^2 - (99^2 - 2 99 + 1) = 2 99 -1 = 197

Akash Singh
Nov 17, 2014

98+99=197 bcoz difference b/w 2 consecutive squares is the sum of those 2 consecutive numbers

Roha Ali
Nov 17, 2014

99 ka square ly gy nd phr usy 98 k square sy (-) minous kr dy gy :)

Muhammad Waqas
Nov 17, 2014

(99+98)(99-98) (197)(1) 197

Akshaya Ravi
Nov 17, 2014

98^2=(99-1)^2

99^2-(99^2-2x99+1)

=2x99-1=197

Anum Parekh
Nov 17, 2014

a^-b^=(a+b)(a-b)
99^-98^ =(99+98)(99-98)

Suraj Lal
Nov 17, 2014

(100-1)^{ 2 }-(100-2)^{ 2 }=((100^{ 2 })-(2 100 1)+1)-((100^{ 2 })-(2 100 2)+(2^{ 2 }))=400-200-4+1=197

Nusrin Habeeb
Nov 16, 2014

(1+98)(1+98)-98^2 =1+2×98+98^2-98^2 =1+196 =197

99^2-98^2 = (100-1)^2 - (100-2)^2 = (10,000-200+1) - (10,000-400+4) =10,000-200+1-10,000+400-4 =200-3 =197

Anna Anant
Nov 16, 2014

Difference of two squares formula: 99^2 - 98^2= (99 + 98)(99 - 98)= (197)(1)= 197

Sajeni Malay
Nov 16, 2014

99^2 - 98^= 9801 - 9604=197

Federico Sony
Nov 16, 2014

99^2-98^2=(98+1)^2-98^2=98^2+2 98 1+1-98^2=196+1=197

Mukesh Dhariwal
Nov 12, 2014

99^2 -98^2 =(99+98) =197

You ccould've shown how you got: 99^2 -98^2 =(99+98).

Ritu Roy - 6 years, 7 months ago

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